Membrane inflation
We use membrane inflation testing to characterize thin elastomeric sheets and soft biological tissues under biaxial loads in addition, or as an alternative, to tensile testing in the biaxial testing device. In facts, inflation experiments produce (a non-homogenous) biaxial state of stress, which in many regards represents the physiological loading conditions of soft biological membranes such as the fetal membranes [1-5] or organ capsules [6,7] more closely as compared to conventional tensile experiments.
Briefly, our custom devices consist of short cylinders on which a thin test piece can be mounted on top [8-10]. The cylindrical cavity is equipped with a pressure sensor, and is filled with air, water or physiological saline, under either volume or pressure control. Time-synchronized CCD cameras on the top and side record images of the inflating specimen and thus allow determining the displacement field in the membrane center and the radii of curvature, respectively.
Different pump types (syringe, peristaltic, gravity) together with control algorithms enable us to realize desired profile of volume or pressure histories such as constant flow, creep or cyclic loads [4,5,11], and custom clamping solutions protect delicate samples from failure at the clamping site [12].
Recent developments make this type of device suitable to tests membranes with an initial defect, by supporting the delicate samples with thin lubricated sheets of an impermeable elastomer [12].
These centimeter-scale inflation devices also inspired the designs of the micromechanical testing devices and bioreactors developed in our lab.
[1] Haller C.M., Buerzle W., Brubaker C. E., Messersmith P.B., Mazza E., Ochsenbein-Koelble N., Zimmermann R., Ehrbar M. (2011) Mussel-mimetic tissue adhesive for fetal membrane repair: a standardized ex vivo evaluation using elastomeric membranes, Prenat. Diagn. 31, 654-660. DOI: 10.1002/pd.2712
[2] Haller C., Buerzle W., Kivelio A., Perrini M., Brubacker C. E., Gubeli R.J., Mallik A.S., Weber W., Messersmith P.B., Mazza E., Ochsenbein-Koelble N., Zimmermann R., Ehrbar M. (2012) Mussel-mimetic tissue adhesive for fetal membrane repair: An ex vivo evaluation, Acta Biomater. 8, 4365-4370. DOI: 10.1016/j.actbio.2012.07.047
[3] Buerzle W., Haller C. M., Jabareen M, Egger J., Mallik A. S., Ochsenbein-Koelble N., Ehrbar M., Mazza E. (2013) Multiaxial mechanical behavior of human fetal membranes and its relationship to microstructure, Biomech. Model. Mechanobiol. 12, 747-762. DOI: 10.1007/s10237-012-0438-z
[4] Perrini M., Mauri A., Ehret A.E., Ochsenbein-Kölble N., Zimmermann R., Ehrbar M., Mazza E. (2015) Mechanical and microstructural investigation of the cyclic behavior of human amnion. J. Biomech. Eng. 137, 061010. DOI: 10.1115/1.4030054
[5] Perrini M., Bürzle W., Haller C., Ochsenbein-Kölble N., Deprest J., Zimmermann R., Mazza E., Ehrbar M. (2013) Contractions, a risk for premature rupture of fetal membranes: A new protocol with cyclic biaxial tension. Med. Eng. Phys. 35, 846-851. DOI: 10.1016/j.medengphy.2012.08.014
[6] Hollenstein M., Mazza E. (2012), Mechanical Characterization of the Human Liver, Eds: Holzapfel G., Kuhl E., Computer Models in Biomechanics: From Nano to Macro, Springer. DOI: 10.1007/978-94-007-5464-5_26
[7] Bircher K., Ehret A.E., Mazza E. (2016) Mechanical characteristics of bovine Glisson's Capsule as a model tissue for soft collagenous membranes. J. Biomech. Eng. 138, 081005. DOI: 10.1115/1.4033917
[8] Hollenstein M. Mechanics of the Human Liver: Experiments and Modeling, ETH Diss. Nr. 19587 (2011).
[9] Bürzle W. Mechanical characterization and modeling of human fetal membrane tissue. ETH Diss. Nr. 21784 (2014).
[10] Perrini M. Preterm rupture of fetal membranes: mechanical characterization and repair strategies. ETH Diss. Nr. 22429 (2015).
[11] Bernardi L., Hopf R., Sibilio D., Ferrari A., Ehret A.E., Mazza E. (2017) On the cyclic deformation behavior, fracture properties and cytotoxicity of silicone-based elastomers for biomedical applications. Polym. Test. 60, 117-123. DOI: 10.1016/j.polymertesting.2017.03.018
[12] Bircher K., Ehret A.E., Spiess D., Ehrbar M., Simões-Wüst A. P., Ochsenbein-Kölble N., Zimmermann R., Mazza E. (2019) On the defect tolerance of fetal membranes. Interface Focus 9, 20190010. DOI: 10.1098/rsfs.2019.0010